In viewing video and computer graphics, particularly animated graphics, the human eye is very sensitive to discontinuities in frame rate. Application programs generally have been able to control their frame rate because they draw directly to the frame buffer, or use hardware hooks to target a particular rate. However, one contemporary operating system being developed by Microsoft Corporation provides a desktop window manager that takes over control of the desktop, whereby application programs no longer present directly to the screen, nor have as direct of access to hardware timing. Instead, the desktop window manager intercepts the graphic updates from application program windows, and combines or composes them on a regular schedule to create the visible desktop. The desktop window manager thus controls when content reaches the screen, and to avoid distracting glitches and tearing, needs to maintain smooth predictable frame rates for the content.
Composing the desktop requires a significant amount of the total computing power available, particularly in the case of graphics capabilities. Previously graphics processing unit resources were used only by application programs; however the desktop window manager requires that graphics resources be balanced among many simultaneous users. Further, as an operating system or otherwise shared component, the desktop window manager has to judiciously use resources so that resources are conserved for use by the application programs.